Can you give an example of what you're trying to search for that does not work?

I just tested over here with both English and French accented words and the forum search seems to be working fine for me, so I'll need more information about exactly what it is you're trying to do to look into it more.

One thing to note is that the French language section is basically organized into a separate forum and the forum search will only search in one forum at a time, so for example if you are currently logged in to the regular English forum and do a search you will not see results from the French forum listed and that's normal, you need to switch to the French forum in order for a search to target those posts.

Search engine
Now that works ! (Firefox)
Not Opera (request menu is there but request gives nothing )

I have a problem with Opera but seems that is not from the new server but from my version because that works fine with Firefox !
I can't acces to the French part (Opera)
I well see the Pop Up menu with the different language but when I click on it nothing is done!

With Javascript disabled you would have actually seen the exact same behavior on the forum on the previous server as well, I guess you probably don't use Opera for your normal daily stuff or else you would have noticed it not working some time ago.

There will be quite a lot of web sites that won't work correctly if you have Javascript disabled.